package org.apache.lucene.search.spans;

/**
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

import java.util.Iterator;
import java.util.Collection;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;

import org.apache.lucene.search.Query;
import org.apache.lucene.search.Weight;
import org.apache.lucene.search.Searcher;
import org.apache.lucene.search.Scorer;
import org.apache.lucene.search.Explanation;
import org.apache.lucene.search.Similarity;

class SpanWeight implements Weight {
    private Similarity similarity;
    private float value;
    private float idf;
    private float queryNorm;
    private float queryWeight;

    private Collection terms;
    private SpanQuery query;

    public SpanWeight(SpanQuery query, Searcher searcher) throws IOException {
        this.similarity = query.getSimilarity(searcher);
        this.query = query;
        this.terms = query.getTerms();

        idf = this.query.getSimilarity(searcher).idf(terms, searcher);
    }

    public Query getQuery() {
        return query;
    }

    public float getValue() {
        return value;
    }

    public float sumOfSquaredWeights() throws IOException {
        queryWeight = idf * query.getBoost(); // compute query weight
        return queryWeight * queryWeight; // square it
    }

    public void normalize(float queryNorm) {
        this.queryNorm = queryNorm;
        queryWeight *= queryNorm; // normalize query weight
        value = queryWeight * idf; // idf for document
    }

    public Scorer scorer(IndexReader reader) throws IOException {
        return new SpanScorer(query.getSpans(reader), this, similarity, reader.norms(query.getField()));
    }

    public Explanation explain(IndexReader reader, int doc) throws IOException {

        Explanation result = new Explanation();
        result.setDescription("weight(" + getQuery() + " in " + doc + "), product of:");
        String field = ((SpanQuery) getQuery()).getField();

        StringBuffer docFreqs = new StringBuffer();
        Iterator i = terms.iterator();
        while (i.hasNext()) {
            Term term = (Term) i.next();
            docFreqs.append(term.text());
            docFreqs.append("=");
            docFreqs.append(reader.docFreq(term));

            if (i.hasNext()) {
                docFreqs.append(" ");
            }
        }

        Explanation idfExpl = new Explanation(idf, "idf(" + field + ": " + docFreqs + ")");

        // explain query weight
        Explanation queryExpl = new Explanation();
        queryExpl.setDescription("queryWeight(" + getQuery() + "), product of:");

        Explanation boostExpl = new Explanation(getQuery().getBoost(), "boost");
        if (getQuery().getBoost() != 1.0f)
            queryExpl.addDetail(boostExpl);
        queryExpl.addDetail(idfExpl);

        Explanation queryNormExpl = new Explanation(queryNorm, "queryNorm");
        queryExpl.addDetail(queryNormExpl);

        queryExpl.setValue(boostExpl.getValue() * idfExpl.getValue() * queryNormExpl.getValue());

        result.addDetail(queryExpl);

        // explain field weight
        Explanation fieldExpl = new Explanation();
        fieldExpl.setDescription("fieldWeight(" + field + ":" + query.toString(field) + " in " + doc + "), product of:");

        Explanation tfExpl = scorer(reader).explain(doc);
        fieldExpl.addDetail(tfExpl);
        fieldExpl.addDetail(idfExpl);

        Explanation fieldNormExpl = new Explanation();
        byte[] fieldNorms = reader.norms(field);
        float fieldNorm = fieldNorms != null ? Similarity.decodeNorm(fieldNorms[doc]) : 0.0f;
        fieldNormExpl.setValue(fieldNorm);
        fieldNormExpl.setDescription("fieldNorm(field=" + field + ", doc=" + doc + ")");
        fieldExpl.addDetail(fieldNormExpl);

        fieldExpl.setValue(tfExpl.getValue() * idfExpl.getValue() * fieldNormExpl.getValue());

        result.addDetail(fieldExpl);

        // combine them
        result.setValue(queryExpl.getValue() * fieldExpl.getValue());

        if (queryExpl.getValue() == 1.0f)
            return fieldExpl;

        return result;
    }
}
